METHODS FOR THE ESTIMATION AND VALIDATION OF MULTICOMPONENT FORMULATION

Abstract:
The aim of the present work was focused on development of analytical methods for the estimation of drugs in multi component dosage form. There is a plethora of analysis of such formulations without prior separation. For the estimation of multi component formulation, the instrumental techniques, which are commonly employed, are spectrophotometry, Gas liquid chromatography (GLC), high performance thin layer chromatography (HPTLC), high performance liquid chromatography (HPLC) etc. These methods are based upon the measurement of specific and non specific physical properties of the substances. Chromatographic separation techniques are one of the most widely used technique for analysis of a multi component formulation. HPLC techniques allows for the separation as well as analysis of different drugs that are present in a combined formulation. Validation studies were performed in order to assess the validation parameters for the analytical method developed in accordance to ICH Guidelines.

Reference ID: PHARMATUTOR-ART-1955

Introduction:
Analytical chemistry is primarily concerned about determining the qualitative and quantitative composition of material understudy. Both these aspects are necessary to understand the sample material. Analytical chemistry is divided into two branches quantitative and qualitative. A qualitative analysis gives us the information about the nature of sample by knowing about the presence or absence of certain components. A quantitative analysis provides numerical information as to the relative amount of one or more of this component. For analyzing the drug samples in bulk, pharmaceutical formulations and biological fluids, different analytical methods are routinely being used.

In non-instrumental, the conventional and physicochemical property are use to analyse the sample. The instrumental methods of analysis are based upon the measurements of some physical property of substance using instrument to determine its chemical composition. The instrumental methods are simple, precise, and reproducible as compared to classical methods. Therefore, analytical methods developed using sophisticated instruments such as spectrophotometer, HPLC, GC and HPTLC have wide applications in assuring the quality and quantity of raw materials and finished products.

1. Spectrophotometric Method:
Absorption spectroscopy is one of the most useful and widely used tools available to the analyte for quantitative analysis. The relation between the concentration of analyte and the amount of light absorbed is the basis of most analytical application of molecular spectroscopy. This method of analysis i gaining importance due to simple, rapid, precise, highly accurate and less time consuming. Spectrophotometric multi-component analysis can be applied where the spectra of drugs overlaps. In such cases overlapping spectra, simultaneous equation can be framed to obtain the concentration of individual component; otherwise multi-component analysis can be applied on any degree of spectral overlap provided that two or more spectra are not similar exactly. Some of the examples are given in table-1.

1.1 The various spectroscopic techniques used for multi-component analysis are as follows

Simultaneous equation method (Vierodt’s method)
Concentration of several components present in the same mixture can be determined by solving a set of simultaneous equation even if their spectra overlap. If Beer’s law is followed, these equations are linier.

Two wavelength method
The method can be used to calculate the concentration of component of interest found in a mixture containing it along some unwanted interfering component. The absorption different between two points on the mixture spectra is directly proportional to the concentration of the component to be determined irrespective of the interfering component.

The absorption ratio method
The absorbance ratio method is a modification of the simultaneous equation procedure. It depends on the property that for a substance, which obeys Beer’s law at all wavelength, the ratio of absorbance at any two wavelengths is constant value independent of concentration or path length. e.g. Two dilutions of the same substance give the same absorbance ratio A1 / A2. In the USP, this ratio is referred to as Q value. In the quantitative assay of two components in admixture by the absorbance ratio method, absorbances are measured at two wavelengths. One being the λ max of one of the components (λ2) and the other being a wavelength of equal absorptivity of the two components (λ1), i.e., an iso-absorptive point.

Geometric correction method
A number of the mathematical correction procedures have been developed which reduce or eliminate the background irrelevant absorption that may be present in the samples of biological origin. The simplest of this procedure is the three-point geometric procedure, which may be applied if the irrelevant absorption is linier at the three wavelengths selected. This procedure is simply algebraic calculations of what the baseline technique in infrared spectrophotometry dose graphically.

Absorption factor method (Absorption correction method)
It is further modification of simultaneous equation method. Quantitative determination of one drug is carried out by E (1%, 1 cm) value and quantitation of another drug is carried out by subtraction absorption due to interfering drug using absorption factors.

Orthogonal polynomial method
The technique of orthogonal polynomials is another mathematical correction procedure, which involves complex calculation than the three-point correction procedure. The basis of the method is that an absorption spectrum may be represented in terms of orthogonal functions.

Difference spectrophotometry
Difference spectrophotometry provides a sensitive method for detecting small changes in the environment of a chromophore or it can be used to demonstrate ionization of a chromophore leading to identification and quantitation of various components in mixture. The essential feature of difference spectrophotometric assay is that the measured value is the difference absorbance (?A) between two equimolar solutions of the analyte in different chemical forms, which exhibits different spectral characteristics.

Derivative spectrophotometry
Derivative spectrophotometry is useful means of resolving two overlapping spectra and eliminating matrix interference due to an indistinct shoulder on side of an absorption bands. It involves conversion of normal spectrum [A= f (λ)]to its first [dA/ dλ = f (λ)], second [d2A/ dλ2 = f (λ)]and higher derivatives spectra where the amplitude in the derivative spectrum is proportional to the concentration of the analyte provided that Beer’s law is obeyed by the fundamental spectrum.

Area under curve method
In this method, the absorptivity values (ε1 andε2) of each of the two drugs were determined at the selected wavelength range. Total area under curve of a mixture at wavelength range is equal to the sum of area under the individual component at that wavelength range. This method is applicable when the λ max of the two components are reasonably dissimilar, the two components do not interact chemically and both the component must be soluble in same solvent.

2. Chromatographic methods:
Chromatography is a technique employed for separation of the components of mixture by continues distribution of the component between two phases. One phase moves (mobile phase) over the other phase (stationary phase) in a continuous manner. When the stationary phase is a solid support of adsorptive nature and mobile phase is liquid or gaseous phase it is called Adsorption chromatography. When the stationary phase is liquid in nature and the mobile phase is liquid or gaseous it is called Partition Chromatography.

2.1 Theory of Chromatography:
Two theoretical approaches have been developed to describe the processes involved in the passage of solutes through a chromatographic system.

1. The plate theory:
According to martin and synge, a chromatographic system consists of discrete layers of theoretical plates. At each of these, equilibration of the solute between the mobile and stationary phases occurs. The movement of solute is considered as a series of stepwise transfers from plate to plate.